i am extremely sorry for the problems you are dealing with! and i am trying to find out if i have a condition similar to yours or not. just as you said, i can't go downstairs, i can't squat on the affected leg and i feel that entire leg unstable, not only the knee, but the hip and ankle also. and i have an extremely big pain all around my knee, not necessarily inside of it, altough i have regained a big part of my muscle mass. when you are trying to plant your foot, do you feel an extremely big pain in your leg that simply makes all of your muscles loose tone instantly? because this is what i feel. i can make the movement in the air ( hardly, though ) but when i plant my foot, the pain around my knee , especially in the medial side under my knee makes all of my muscles loose their tone and i feel my entire leg unstable. does anyone else experience this thing? best wishes for all of you !